This invention relates to sleeve inserts for the cylinders of a reciprocating piston apparatus, and particularly to the manner of joining a sleeve insert to the cylinder.
The trend in the development of internal combustion engines is to reduce the weight of the engine by using aluminum or aluminum alloys instead of the traditional cast iron for the cylinder block and other major engine components. The use of aluminum makes it necessary to provide a wear surface for the cylinder bore of some other harder material since most aluminum is too soft to withstand the abrasion that will be encountered as the piston works in the cylinder. The harder surface for the cylinder is typically provided by a thin wall cast iron sleeve insert for the cylinder.
The cast iron sleeves have been mounted within the cylinders by several techniques. One approach uses a sleeve formed with an external pattern of protrusions or ribs. The preformed sleeve is placed into the mold for casting of the cylinder about the sleeve. A second approach has been to shrink fit the sleeve into the cylinder. Both approaches achieve less than satisfactory results primarily because they require the application of heat to one or both of the sleeve and cylinder during the assembly. The heating of the components and the insertion of the sleeve greatly increasing the production time. More importantly, upon cooling the cylinder bore becomes distorted because of uneven expansion or contraction in the thin wall sleeve. If such distortion is sought to be eliminated by reboring the sleeve following its assembly into the cylinder, uneven wall thicknesses for the sleeve will result. The heat transfer from the sleeve to the cylinder during operation then becomes non-uniform and localized and results in different, unacceptable distortions to the cylinder bore.
The normal machining operations required on a thin wall sleeve can also distort the sleeve even if the sleeve is not subjected to differential heating or cooling. The gripping of the sleeve during machining and the normal tool forces can result in unacceptable distortions.
Although these problems involving the use of sleeve inserts are particularly acute in the manufacture of internal combustion engines, similar problems are also present in connection with sleeve inserts for other reciprocating piston equipment, such as air compressors.
The present invention is directed to the manner of mounting a sleeve insert in a cylinder which does not require the application of heat or cooling during the assembly process, which allows the complete production of the sleeve prior to its assembly in the cylinder without distortion, and which allows the sleeve to be assembled or disassembled from the cylinder at room temperature using simple tools.